(1) Field of the Invention
The present invention relates to a process for producing a novel contact lens having a number of microfine through-holes which do not impair the basic properties and functions of contact lens and accordingly exhibiting very high oxygen permeability.
(2) Description of the Prior Art
Contact lenses, as well as conventional spectacles, are in wide use as a means for eyesight correction.
Contact lenses are used on the cornea in direct contact therewith. Therefore, they are required to not only have sufficient optical properties for eyesight correction and good physical and chemical stabilities but also to provide good feeling when worn and enable long continuous wear.
Since the cornea with which a contact lens is in direct contact is an avascular tissue, the cornea tissue, particularly its epithelial tissue takes in oxygen (necessary for the metabolism) from the air via lacrima. Accordingly, in order for a contact lens to provide good feeling when worn and enable long continuous wear, the contact lens must satisfy a requirement that a sufficient amount of oxygen be supplied to the cornea tissue even when the lens is worn. Hence, a contact lens giving better feeling when worn and enabling long continuous wear has been studied through an approach of developing a contact lens with improved oxygen permeability.
As the method for obtaining a contact lens with improved oxygen permeability, there are (a) a method wherein an improved material for contact lens is used (for example, an oxygen-permeable substance is used as a material for contact lens, or, a highly water-absorptive polymer is used as a material for contact lens to allow the material to indirectly have higher oxygen permeability) and (b) a method wherein through-holes are formed in a contact lens to allow the contact lens to have higher oxygen permeability. The latter method (b) can provide a contact lens of higher oxygen permeability irrespective of the type of material used, as compared with a contact lens using the same material but having no through-holes (see, for example, Journal of Japanese Contact Lens Association 25, pp. 191-200, 1983), and therefore is drawing attention.
The method for forming through-holes in a contact lens includes a mechanical holing method and a method wherein a monomer or monomers are polymerized in a vessel containing a fibrous substance aligned in one direction and, after molding the resulting polymer into a contact lens, the fibrous substance contained in the polymer is removed [for example, Japanese Patent Application Kokai (Laid-Open) Nos. 161436/1981 and 48022/1983].
When through-holes are formed according to these conventional methods, however, the sizes of through-holes are usually as large as several hundred microns or more and their number is as small as about several to 10; accordingly, the effect of oxygen permeability improvement by through-holes formation is insufficient. Thus, the through-holes formation by the conventional methods have been unable to fully satisfy the better feeling when worn and the longer continuous wear both of which are current requirements for contact lenses. Further, the large through-holes formed by the conventional methods significantly reduce the optical and mechanical properties originally possessed by contact lens materials, making it difficult to obtain a practical contact lens.
Hence, in order to obtain a contact lens which has excellent oxygen permeability and yet can be used practically, it is necessary to significantly improve oxygen permeability by through-holes formation and further to prevent the reduction in optical and mechanical properties caused by the conventional through-holes formation methods.